The other day, an idea dawned on me. It took several hours before the full weight of it began to sink in. It's an idea that has enjoyed constant employment by the human imagination, so much so that the terror of it has been weakened from banality. When I was forced to take it out of fantasy books and in to reality, I wasn't so sure I liked it.
It occurred to me, that it might be possible to make a device that causes light to travel in closed causal curves. As in, I could do some calculations and tell you how to make it and someone with a nanolab could build it in a year or so. This would allow communication with the future through radio waves; you broadcast them in to the machine and into the future, the future responds by broadcasting into the past.
When I say that it might be possible, let me stress the might. While technically the laws of physics do not prohibit the existence of such things, most physicists tend to discount them as requiring physically impossible constructions like infinite cylinders. The reality, is that I don't know enough to know whether there are any physical constraints that would prohibit closed causal curves in the situation I'm considering. There probably is; if not theoretical constraints, then certainly physical constraints.
My point isn't whether it's possible or not, and it most likely isn't; my point is really more about the terrifying implications if it is.
So imagine this: there is in front of you, placed on a table, a small cubic device whose construction you have now completed. You turn it on. At once, a smattering confusion of voices overtakes the static of the device's radio. Slowly these die off, all but one voice remaining. Your own voice; yet not your voice, not any words you have ever spoken, but words that you will, someday, speak.
And imagine, a hundred years after it has been turned on, when people alive to see it have died. People have spoken words in to it, heard reply from the future, then later passed on from this world. Yet the light containing their words remains trapped in the machine, and now is emitted and played over the device, a hundred years and yet mere seconds after they were spoken. You reply to them, and across the years they hear you and respond in turn.
These lost voices somehow heard your reply before it was ever uttered.
I dunno. It gives me the creeps thinking about it. It just sounds too much like talking to a ghost.
And who are you talking to then you send a message to yourself, ten minutes in to the future? Can you ever be sure that the voice that replies is your own? Or even that it is of any human agency?
If the future sends you warning of a catastrophe that has befallen there, and you in the past avoid it... then whose warning did you heed?
Maybe I need to stop reading so much speculative fiction... what more after all is a mad scientist than the quixotic knight of the present?
Edit: The original version of this referred to light moving on closed timelike curves, which of course is impossible because light doesn't move on timelike curves, closed or not. What I meant was causal curves. This has been fixed.